FR2771813A1 - VOLUME COUNTER OF A FLOWING FLUID - Google Patents

Abstract

Volume meter of a flowing fluid According to the invention, said meter comprises: - a viscosensitive element (10) through which said fluid passes according to a laminar flow regime, - a first fluidic oscillator (21) in series with said fluid. viscosensitive element (10), - a second fluidic oscillator (22) in parallel at least on the viscosensitive element (10), the viscosensitive element (10) and said fluidic oscillators (21, 22) being able to determine the viscosity of the fluid, so as to provide the volume of fluid measured by the fluidic oscillators (21, 22) with a correction depending on the number of Reynolds. Application to the precision measurement of the volume of fuel.

Description

VOLUME COUNTER OF A FLOWING FLUID

  The present invention relates to a volume meter of a flowing fluid.

  The invention finds a particularly advantageous application in the field of precision measurement of the volume of fluid delivered by a dispensing device, in particular a fuel dispenser. Fuel distribution devices are equipped with a device for measuring the volume of fuel delivered. This organ, called

  also a measurer, is generally a mechanical meter of the volumetric type10.

  The function of a mechanical measurer is to produce a rotational movement from the flow of fuel, one complete revolution of which corresponds to a given volume of fuel passing through the measurer. We know for example the piston meter15 in which the liquid from the distributor pump is injected into 2 or 4 cylinders which are filled and emptied successively by means of a dispensing drawer device. The pistons actuate a crankshaft whose angle of rotation is proportional to the volume of liquid which has passed through the cylinders. An optical or magnetic encoding system20 coupled to the rotational movement provides an electrical signal consisting of a series of pulses, each of which

  corresponds to the volumetric measurement step, lcl for example.

  The piston / cylinder volume meter technique has been well mastered for many years, but it nevertheless has a certain number of drawbacks, namely: - numerous mechanical parts, - tight machining tolerances, - large dimensions, - parts made of movement presenting phenomena of wear by friction which must be compensated by periodic calibrations, - problematic behavior of materials with chemical components contained in fuels, - mechanical noise, - large internal volume not allowing to make

  sequential counting of several products in the same counter.

  Also, the technical problem to be solved by the object of the present invention is to propose a volume meter of a flowing fluid which would make it possible to remedy the drawbacks presented by known mechanical meters, in particular by limiting the

number of moving parts.

  The solution to the technical problem posed consists, according to the present invention, in that said counter comprises: - a viscosensitive element traversed by said fluid according to a laminar flow regime, - a first fluidic oscillator in series with said viscosensitive element, a second fluidic oscillator in parallel at least on the viscosensitive element, the viscosensitive element and said fluidic oscillators being able to determine the viscosity of the fluid, so as to bring to the volume of fluid measured by the fluidic oscillators a dependent correction

of the Reynolds number.

  Thus, the volume meter according to the invention has no moving parts, which eliminates all the problems of wear and noise. Just as it is simple mechanical construction, compact, economical, and insensitive to pressure variations and vibrations. Finally its low internal volume allows counting

  sequential of several fuels.

  Recall that a fluidic oscillator is a so-called static counter 3 in which the fluid whose volume we want to measure flows through a cavity designed to cause a periodic oscillatory movement of the fluid flow. The frequency of

  fluid oscillations is a first approximation proportional to the flow rate of the fluid passing through the oscillator. The precision obtained is of the order of + 2%. In many cases, this precision is sufficient.

  However, with regard to fuels, the current legislation requires a much greater precision of + 0.3%. It is then necessary to take account of a corrective term depending on the Reynolds number of the fluid in the oscillator. The determination of the Reynolds number requires that of the viscosity of the fluid, this is precisely what makes it possible to obtain

  the arrangement of the volume meter of the invention, according to the principles described in French patent application No. 97/15042. The following description next to the accompanying drawings,

  given as nonlimiting examples, will make it clear how

  consists of the invention and how it can be realized.

  Figure 1 is a schematic sectional view of a fluidic oscillator. FIG. 2 is a diagram giving the variations in the number of oscillations per liter of the fluidic oscillator of FIG. 1 as a function

of the Reynolds number.

  FIG. 3 is a diagram of a first embodiment of a

  volume meter according to the invention.

  Figure 4 is a diagram of a second embodiment

  a volume meter according to the invention.

  Figure 5 is a schematic sectional view of the counter of

volume of figure 4.

  FIG. 6 is a diagram giving the variations over time of the signal coming from the fluidic oscillator of FIG. 1 and of the

  corresponding signal from a shaping circuit.

  FIG. 7 is a block diagram of the means for correcting the

  volume measurement as a function of Reynolds number.

  In Figure 1 is shown in section a fluidic oscillator 20 whose principle, known per se, consists in passing a fluid through a cavity designed so that the fluid passing through it is subjected to periodic oscillatory movements. A faithful relationship links the frequency of the oscillations to the flow rate which passes through the cavity. An electronic device transforms the periodic signal supplied by the fluidic oscillator into pulses corresponding to the volumetric measurement step. The pulse count gives a direct measurement of the volume, making the fluidic oscillator a

volumetric meter.

  It can be seen in Figure 1 that, conventionally, the fluidic oscillator 20 includes a first cavity 201 serving as flow conditioner. Indeed, the incident fluid can be subjected to internal speed distributions depending on the installation and risking disturbing the measurement. The fluid flow strikes an obstacle 203 which directs the flow in a controlled manner towards a calibrated slot 204,

  regardless of the pipeline placed upstream.

  The slot 204 makes it possible to inject the fluid at high speed into a second cavity 202 comprising a second obstacle 205 which deviates the flow alternately either to the right (continuous arrow) or to the left (dotted arrow). Circulations of fluid are created inside the cavity 202 which react on the jet at high speed, forcing it to change direction. The phenomenon reverses periodically as a function of the fluid flow rate Q. The detection of the change in direction of the jet by sensors 206, 207 therefore makes it possible to measure the frequency F of the oscillations and to know the flow rate Q. For a given flow rate Q, the frequency F is perfectly stable, reproducible and faithful. It is therefore possible to know the volume of fluid delivered corresponding to each elementary oscillation. The sensors 206, 207 are, for example, preheated thermal probes of which the resistance variations induced by the speed variations of the fluid in contact with the probes are detected. The probes 206, 207 are supplied by a regulated current5, which leads them to heat up by the Joule effect and to bring their temperature to a value higher than that of the fluid. In this case, the passage of the fluid jet results in the evacuation of the heat generated

by the probes.

  As a first approximation, the frequency F of a fluidic oscillator is proportional to the flow Q of the fluid:

F = KQ (1)

  K being a characteristic coefficient of the fluidic oscillator.

  However, as shown in Figure 2, we can observe that the coefficient K of the relation (1) depends for a given flow Q, on the Reynolds number Re of the oscillating cavity 202 Re = Q / hv

  where h is the height of the cavity and v the kinematic viscosity of the fluid.

  The dispersion of the coefficient K as a function of R can reach

  + 2%, which may be acceptable in a large number of situations.

  However with regard to the measurement of the volume of fuel delivered by

  a distributor, the precision imposed by the Administration is + 0.3%.

  The variations of K with the Reynolds number can be represented by the relation: K = Ko (1+ c (Re)) o Ko is an average value and Ko e (Re) the deviation to Ko for the number of

  Reynolds Re. In Figure 2, Ko is 50 oscillations / liter.

  The relation (1) is then written: F = Ko (1 + c (Re)) Q (2) If qo is the average elementary volume corresponding to an oscillation of frequency F (qo = 1 / Ko) and if q is the real elementary volume 6, the relation (2) is written with c (Re) small before 1: q = qo (lE (Re)) (3) Taking into account the dispersion of the coefficient K as a function of the number Re de Reynolds therefore amounts to correcting at each oscillation the elementary volume qo of the quantity qo E (Re). Since the Reynolds number depends, for a given oscillating cavity, essentially on viscosity, it is absolutely necessary to

  ability to measure viscosity of fluid in real time.

  For this purpose, as shown in FIGS. 3 and 4, there is provided a counter for the volume of flowing fluid comprising: - a viscosensitive element 10 traversed by said fluid according to a laminar flow regime, - a first fluidic oscillator 21 in series with said viscosensitive element 10, - a second fluidic oscillator 22 in parallel at least on the viscosensitive element (10), the viscosensitive element 10 and said fluidic oscillators 21, 22 being

  able to determine the viscosity of the fluid.

  The way in which the volume counters of FIGS. 3 and 4 make it possible to measure the viscosity of the fluid is explained in detail in French patent application No .............. Let us only recall that: - in the case of FIG. 3 o the second fluidic oscillator 22 is placed in parallel on the only viscosensitive element 10, the dynamic viscosity pt is given by: t = (a2 / k) x2 Qt / (1- x) (4) ox is the ratio QI / Q2 of the flow rates measured by the fluidic oscillators 21, 22, Qt is the total flow rate, here Q1, and where a2 and k are characteristic parameters of the second fluidic oscillator 22 and of the viscosensitive element 10, the ratio (a2 / k) is known by prior calibration. Kinematic viscosity v is related to dynamic viscosity

  k by v = g / p, p being the density of the fluid.

  - in the case of FIG. 4 o the second fluidic oscillator 22 is placed in parallel on the assembly constituted by the viscosensitive element 10 and the first fluidic oscillator 21, the dynamic viscosity H of the fluid is given by: = (1 / k) (a2x2 - al) Qt / (x + 1) (5) ox is the ratio QI / Q2 of the flows measured by the fluidic oscillators 21, 22, Qt is the total flow QI + Q2, and where QI is a characteristic parameter of the first fluidic oscillator 21, the ratios al / k and

  a2 / k being known by prior calibration.

  The viscosensitive element 10 is arranged so as to ensure a laminar regime of the fluid over the entire range of flow rates envisaged. An exemplary embodiment of such a viscosensitive element is provided by the

  flame arresters used in fuel dispensers.

  FIG. 5 shows a particular embodiment of the meter shown diagrammatically in FIG. 4. As may be noted, a flow reduction diaphragm 30 has been placed in series with the second fluidic oscillator 22, this for reasons for balancing flows between the two branches. The presence of the diaphragm 30 has the effect of increasing the parameter a2 of the second

fluidic oscillator 22.

  Figure 6 shows the plowshare signal supplied directly by a fluidic oscillator. In the case of an oscillator with two sensors 206, 207 as illustrated in FIG. 1, the soc signal is the differential signal of the two sensors. Compared with Soc, an impulse signal Imp deduced from sosc is represented by an electronic shaping circuit, known per se. Each impulse of Imp corresponds to the actual elementary volume q of the fluid, the summation over all the impulses of the

  actual elementary volumes q gives the total volume of the fluid flowing.

  The volume meters in Figures 3 and 4 operate from the

8 next way.

  The flow rates QI and Q2 of fluid passing through the fluidic oscillators

  21, 22 are determined from the approximate formulas.

  Q - qoi F1 and Q2 - qo2 F2 Knowing Qi and Q2, we know x and Qt from which we can deduce the dynamic viscosity t and, and therefore the kinematic viscosity v, by the formulas (4) and (5) applied either analytically , or in the form of tables, after calibration. For each fluidic oscillator, we can then calculate the corresponding Reynolds number, namely: Rej = QI / hlv and Re2 = Q2 / h2v Then, knowing by calibration the corrections El (Rel) and $ 2 (Re2), it is possible to determine the actual elementary volumes corresponding to a pulse of the signals Impl and Imp2: 15 ql = qo (1- El (Rel)) q2 = qo2 (1- c2 (Re2)) This correction operation is carried out by a microprocessor shown in the FIG. 7. A counter 200 performs the pulse-by-pulse summation of the actual elementary volumes ql and q2 to obtain the total volume of fluid flowing and each time that an elementary volume qo, for example lcl, is counted, the counter 200 provides a impulse Imp 'to a computer, like the computer of a fuel distributor, which only has to count the impulses Imp' to determine the volume of fluid flowing. As a variant, the counter 200 could just as easily provide the total accumulated volume,

  sent periodically in coded form.

  Some official bodies request that the volume be corrected in temperature. Indeed, the volume of a fluid, in particular the hydrocarbons, varies from approximately 0.1% per degree, and, the temperature varying between -20 ° C. and 35 ° C., the relative variation in volume of the fluid can reach 5%. The thermal probes 206, 207 can then be used to also measure the temperature of the liquid, the

  volume correction being carried out by microprocessor 100.

Claims (5)

  1 - Volume meter of a flowing fluid, characterized in that it comprises: - a viscosensitive element (10) traversed by said fluid according to a laminar flow regime, - a first fluidic oscillator (21) in series with said viscosensitive element (10), a second fluidic oscillator (22) in parallel at least on the viscosensitive element (10), o the viscosensitive element (10) and said fluidic oscillators (21, 22) being able to determine the viscosity of the fluid, so as to provide the volume of fluid measured by the fluidic oscillators (21, 22) with a   correction depending on the Reynolds number.   2 - Meter according to claim 1, characterized in that the second fluidic oscillator (22) is placed in parallel on the only viscosensitive element (10).   3 - Counter according to claim 1, characterized in that the second fluidic oscillator (22) is placed in parallel on the assembly formed by the viscosensitive element (10) and the first oscillator fluidics (21).   4 - Counter according to any one of claims 1 to 3,   characterized in that a diaphragm (30) is placed in series with at   minus one of the two fluidic oscillators (21, 22).   - Counter according to any one of Claims 1 to 4,   characterized in that the fluidic oscillators (21, 22) are provided with   preheated thermal probes (206, 207).   6 - Counter according to any one of claims 1 to 5,   characterized in that it comprises means for correcting the volume of   fluid as a function of temperature.